Sedimentary Rocks

What are we doing today? Objective – I can describe how the processes of weathering, erosion, and deposition contribute to the formation of sediments, sedimentary rock and landforms.

Sedimentary Rocks Sediments are loose materials such as rock fragments, mineral grains, and bits of shell that have been moved (erosion) by wind, water, ice, or gravity. Sediments come from already-existing rocks that are weathered and eroded. Sedimentary rock forms when sediments are pressed and cemented together, or when minerals form from solutions.

Sedimentary Rocks Rocks are weathered into sediments Sediments erode Sediments are deposited Sediments are compacted and cemented

Sedimentary Rocks 75 percent of the rocks exposed at the surface are sedimentary rocks. Sedimentary rocks often form as layers. The older layers are on the bottom because they were deposited first.

Types of Sedimentary Rocks Clastic: made up of fragments from preexisting rocks Chemical: forms from minerals that precipitate from a solution or a suspension Organic: forms from the remains of plants and animals

Clastic Sedimentary Rocks Formed from broken fragments of other rocks, which are created by weathering, and then moved by erosion

Chemical Sedimentary Rocks Minerals collect when seas or lakes evaporate. The deposits of minerals that come out of solution form sediments and rocks. Chemical sedimentary rocks are not made from pieces of preexisting rocks. Examples are limestone and halite.

Organic Sedimentary Rocks Rocks made of the remains of once-living things are called organic sedimentary rocks. Chalk is another organic sedimentary rock that is made of microscopic shells. Another useful organic sedimentary rock is coal.